An oscillator is a circuit that continually and automatically switches between two states. Oscillators are a widely used type of electronic circuit. Many of the oscillators used in electronic circuits are “crystal oscillators”. In a crystal oscillator a crystal is used to control the frequency of the oscillator, that is to control the rate at which the oscillator switches between states.
Crystal oscillators are used in many electronic systems to provide a series of timing pulses that are used by various other components in the system. In crystal oscillators a quartz crystal controls the frequency of a bi-stable circuit that switches between two states.
Low frequency oscillators consume a relatively small amount of power; however, high frequency oscillators consume a relatively large amount of power. Many electronic systems include a relatively low frequency oscillator that is constantly operating and a high frequency oscillator that is turned off when the high frequency circuits in the system are not is use.
For example, in a portable electronic device such as a portable computer, there may be a relatively low speed oscillator which provides timing pulses for some of the logical circuitry such as a microprocessor and there may be a second relatively high speed oscillator that provides pulses for high speed circuitry that transmits and receives radio signals. In such an environment, the radio frequency circuitry may only be used intermittently. For example if the radio frequency circuitry is used to transmit signals from a wireless mouse or a wireless keyboard to the processing unit, the high frequency oscillator may be turned off between key strokes or between movements of the mouse.
Many high frequency circuits (and some low frequency circuits) require clock signals that have a high degree of purity and uniformity. That is, the clock pulses must be of uniform size and shape. Pulses that are shorter than the specified length can produce errors in the logical circuitry which utilizes the output of the oscillator. That is, non uniform clock pulses may cause logical anomalies. For example, circuits may change state at incorrect times or they may not change state at appropriate times. Herein, clock pulses that are shorter or smaller than normal clock pulses are termed “runt” pulses. Runt pulses from an oscillator can cause anomalies in logical circuitry which utilizes the oscillator output.
Frequently, an oscillator will produce runt pulses when the oscillator is started or when the oscillator is turned off. This becomes particularly troublesome in situations when the oscillator is repeatedly, and relatively quickly, turned on and off. The present invention is directed to eliminating runt pulses that may occur when an oscillator is turned on or off.